U.S. Pat. No. 4,746,634 (Danielson) discloses glasses having borosilicate compositions developed for production of microsheet to be used in cover glasses on solar cells. The cover glasses are strongly resistant to solarization, exhibit a cutoff value of 50% at 370 nm. for ultraviolet (UV) radiation, and have properties adapted to forming microsheets.
The glass compositions disclosed in the Danielson patent consist essentially of, expressed in terms of weight percent on an oxide basis:
SiO.sub.2 59-63 ZnO 6.5-7.5 B.sub.2 O.sub.3 8.75-10 CeO.sub.2 4-6 Al.sub.2 O.sub.3 2-2.5 TiO.sub.2 1-3 Na.sub.2 O 6.75-7.75 CeO.sub.2 + TiO.sub.2 6-8 K.sub.2 O 6.25-7.0 Sb.sub.2 O.sub.3 0-0.5
A commercial glass, based on these composition ranges, was developed that has proven eminently satisfactory for use in producing microsheet cover glass for solar cells. Recent developments in solar cell use, particularly for space vehicles or a station, have imposed severe limitations on cover glasses for such cells.
One such requirement is to provide as great a solar spectral transmission as possible. This is necessary to provide maximum efficiency in solar cells used to provide power to space vehicles. It is a purpose of the present invention to provide a cover glass improved in these respects, and a solar cell embodying such cover glass.
In this regard, another purpose is to provide a glass having a sharp cutoff in the UV portion of the spectrum. This maximizes solar intensity while still protecting an organic adhesive against deterioration by shorter wavelength, UV radiation.
Finally, the possible danger of a static electrical discharge in a space vehicle imposes a requirement of a lower bulk electrical resistivity in the glass. This is necessary to aid in reducing buildup of static charge on the space vehicle. It is, then, another purpose to provide a cover glass having a low bulk resistivity.
Over and above providing these several improvements, it has also been required that the properties described in the Danielson patent for forming microsheet glass be at least retained, and preferably improved. A final purpose, then, is to reach this desired end.